<unit, humour> About 31 mm (one inch). "atto-" is the standard SI prefix
for multiplication by 10^-18. A parsec (parallax-second) is 3.26 light-years; an
attoparsec is thus 3.26 * 10^-18 light years. Thus, one attoparsec per
microfortnight is about one inch per second.
This unit is reported to be in use (though probably not very seriously) among
hackers in the UK.
AT&T Bell Labs « attenuation « atto- « attoparsec
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